libomxil: Fix up commercial license flag

The commercial license flag on libomxil is set because it may include
the Adaptive Multi-Rate audio codec (AMR) using FFmepg, which is patent
encumbered.

It turns out this component is disabled by default in the recipe; add a
PACKAGECONFIG to enable it and trigger the "commercial" LICENSE_FLAGS on
it. This make the default build configuration clean unless a user
specifically asks for AMR support, and prevents them from marking the
recipe with the "commerical" flag unnecessarily which could hide
potential problems later on.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>